Conventionally, vehicle speeds are measured using active means such as a “radar gun”. A radar gun emits a wave of a known frequency which reflects from a moving target back to a sensor on the radar gun. The device measures the Doppler effect caused by the motion of the vehicle, and uses this to estimate the speed of the vehicle. This measurement can be made inaccurate by the presence of other vehicles in close proximity to the target; the emitted wave cannot distinguish between vehicles. Furthermore, this approach will only measure the relative speed between the target and the emitter/sensor, and not the speed of the vehicle relative to the road on which it is travelling, which could be at an angle to the direction of the emitted wave.
There is therefore a need to provide a method of determining the speed of a vehicle relative to the road on which it is travelling that can preferably distinguish between multiple vehicles.
According to a first aspect of the present invention, there is provided a system for measuring the speed of a vehicle according to claim 1.
According to a second aspect of the present invention, there is provided a method of measuring the speed of a vehicle according to claim 18.